Note: Descriptions are shown in the official language in which they were submitted.
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~7~:43
This inventi~l relates to the ~ydrotreating of pyrolysis gasoline or
dripolene.
In the ~ydrotreating of a pyrolysis gasoline or dropolene (the terms `
are interchangeably employed), the reaction pressure is gen~erally in the
order of 600 to 1,000 psig depending on the ~eedstock. Th~ hydrog~n
containing gas en~loyed for the hydrotreating is generally obtained from an
olefin plant and s~ch gas is generally available at a pressure of in the
order of 400 psig, thereby necessitating the use of a booste~ compressor
for feeding such gas to the hydrotreating operation. ~
It has now been found that the hydrotreating can be efected at lower
pressures; e.g., in the order of 200 to 400 psig; however, the use of such
lower pressures severely limits the abillty to achieve high hydrogen~partial
pressures. which, based~on reaction;kinetics, should be r~xImized.~ ~ `
The present irvention accordingly provides an;improved process
for the hydrotreating of a pyl'olysi6 gasoline. T~e hydrotreating of a
pyrolysis gasoline proceeds at increased hydro~en partial pressures and
makes possible efective hydrotreating o pyrolysis gaso~ines at lower
i total pressures~ !;~
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1097243
In accorda~ce wLth the present In-.rentlor~ thcre 1~ provlded a proce~s for
hydrotreating a pyrolysLs gasolLne whereLn fr~sh feed pyroly~Ls g~sollne,
hydrogen containLng gas and recycle hydr~treated efflu~nt are contacted Ln ~ ,
hydrotreatLng ~one tf~ produce a hydro~eated e~fluellt, Llghter component~
ar~ sepa~ated from all or the recycle portion of the l~ydro~eated effluent to
reduc~ or eliminate the total quantil~y of lighter components present Ln the
recycle portion of the hydro~eated effluent, Applicant has found that by .
separating lighter component~ from the recycle portLon of the hydrotreal:ed
e~luent th~re i~ obtaLned, at a given total reactlon pre~sure, an increased :~
hydrogen partiaL pressure. ~ i
Whi1e it is not our wish to 1~t~ the invention ~y ~
theoretical reasonLng, it i5 considered that by separatin~ or 1 ~ t~e ~ :
recycle effluent witb respect to lighter components, the leaned recycle efIl~r t
:functiorLs as an absorbing oil to restrlet volatization of light hydrocarbons and .
to remove dew poirlt hydrocarbons in the hydrogen rich vapor existLng in the
react~r thercby resulting in hlgher hydrogen partLal pre~sur~. Thus, :at a
: ~
given total reactor pressure, it i8 possible to maxLmize the h~droge~ partial
pressure.
The :recycle effluent is leaIled of lighter components, i, e., C5 and
ligh~er h~drocarbons. ~general, the h~drotreated ef~lucnt i8 treated to
reduce the conter~t of ~5 ~d lLg~r hydrocarbon~ in an amount whereby~at
least 5 mol ~0, preferably~at least 10 mol %, anà most preferably at lea~t
2Q mol ~0 of the (: 5 and lighter }ydrocarbo~ axe removed from the portion of
the e~fl~ent which is to be rec~rcled to the hydro~0ating re~ctor. A~ ~hould
be ~pparent, it is pos~lble to effect 100% removal s~f C 5 and lighter hydro~
carbon~; hovrever, as apractical matter, In general, such 100% removal i8
not effeeted, wLth the (:! 5 and light~r hydroca~bon r~moval generally belng n
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109~Z43
greater than about 70 mol %. The greater the amount of C5and ll~hte9-
h~drocarbon removal, the grea~r the Inerea,~e In hydrogen partlalpres~ure
in the hydrotreatLIlg reactor. It iB to be understood that cornponent~ which
boil above C5 may also be removed from the effluent or recycle portion
during the separation.
The reduction in C 5and lower boi1ing tlydrocarbnns may be e~fected by
any one of a wide variety of procedures. In accordance with a pxe~erred
procedure, C 5and light~r hydrocarbons are flashed from the effluent or iErom
the recycle portion. The flashing may be supplemented by s~ipping of such
lighter components; e. g., by the use of a hydrogen containing ga~ recovered
from the kydrotreating reactor. As hereinabove noted, other components
may also be sep~rated from the liquid effluent or recycle liq!lid effluent porti n
daring sueh flashing or stripping9 provided thatthe operation ef~ects th2
reduct~on ~ the content of C 5and lower boLling components. The selection o~
a suitable means of e~fecting such reduction ~hould be a~parent to those æ~ille
in the art from the teachings herein. ~ ~:
The h~rdrotreating of the pyrolysi~ gasolille iæ generally eff~cted at
conditions known in the art, except that by proceeding in accordance ~ith the
present inven~ion, it is possible to operat~ at lower total pressures, whLle
simultaneously employ-Lng suitable hydrogen partial pres~ures, Alth~ugh the
present invention is particu~ y ~uitable for operation a$ lower pre~sureB
(in the order of 200 to 400 psig), it is to be understood that the Invention i~
aLso applicable to .~he higher total, pres~ures genarally employed in the art.
The hydrotreating of pyroly6is ga oline is generally effeeted with a ~
hydrogen containing gas (the gas generally contains rom 50% t~ 100%, and :
most general1 om 90% to 95~0 oi hydrogen) at roaot~r inlet temp-rature~
o~ 3 ~
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frv:~ 120"F to 400~, and ~t tot~l reactor pres~ure~ of ~rom 200 to 800 p6ig,
wLth the pres~nt lnventLon, a~ herelnabolre no~d, belng pr~erably ~ffocted
at totaLI pre~ur~ o fro~n 20a to 400 p~lg. The hydrogen l~ generally
emplo~d Ln an am~nt whlch L~ in excess of the ~olchLoxne~lc requLrement~,
wLth such excesses generaLly bein~ Ln the ord,er of from 10 to 50% ovex that
r~qulr0d to ~aturat~ one double bond of the conjugated dL o7efLns and ~tgren~s~
Ln the eed. In general, the ~r~perature rL~ through the reactor L~ in the
ord~r o ~rom 50F to 1V0UF,
In aecordance wLth the present lnventLon, it L8 possible t~ achleve log
mean h~rdrogan partLal p~ ure~ In the order of from 135 to 510 p~ig at total
pr~ s Ln th~ order of from 20~ to 800 psLg, ~rlth the log ~ean hydrogen
parti~l pres~ure~ beLng Ln the order of from 135 to 260 psig at ~t~L pr~s~ure
In the order of from ~00 to 400 p5ig,
The ~ecycle hydrol~eated e~fluent l~ generally employed in an amount
pro~ride recycle b~ f~e h ~ed ratlo~ of ~om 1:1 to 10,1 basls. Aecyele of :
cfflueht 1~ praetLced tt, con~ol the exother~Lc tempera~re rise acro~ the
raact~r bed, FurthermoreJ b~r ~arying the heat removal fro~ the recycle ~1;r ,
the reactLon l:~mpera~re level c:an be adJu~ted.
In aceordanc0 with the pre~nt invention, the recycle when leaned (i. e,,
d~nuded o~ volatLle component~) wlll ab~orb dew point hydrccarbo~ ~rom`the :
h~rog~n rLch vapor phase and maLntaLn the remainLng volatLle compon~sts in
the ll~quld pha~e, thereby IncreasLng the hydrogen partlal pressure in the
h~drotreatlng reactor.
Th~ hydrotreatLng Ls eff0cted in th~ preaence of a ~uitable hydrotr~atLng
c~t~Llyat. T~ hydro~eatlng cat~ly~t can be a noble metal catalyst; e. g., ;
palladill~n with o~ wLthout mod~lers supported on alumina or a non~noble
~etal catal~t, such il~ nLckel aloneJ or in combination wlth b~ngsten or moly
bdenu3n or a cobalt~mol~bdenum catalyst. The cataly~t~ whLch are sul~le
or th~ h~rdrotreatLng of p~olysL~ gasollnes are known lrl the art and the
~electio~ o~ a ~uLtable catalyst L~ deemed to be well within the ~cope OI those
skLlled Ln the art,
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~e~997;~3
The Lnventio~ will be further descrlbed wlth re~pect to the accompanylr g
drawings wherein:
Figure 1 is a simplified schematic 10w diagram of an ~mbodiment of
the present invention and Figure 2 i~ a sim;pl~ied schematic flow diagram o~
a mod-~ication o the embodirnent o:E Figure 1,
Referring now ~ Figure 1, pyrolysis gasoline, in li.ne 13 i8 admL~ed
with recycle leaned hydrotreated effluent, in line 14, obtained as hereinafter
described, and the combined ~tream i5 introduced through line 15 Ln~o a
hydrotreating reactor 11, containlng a bed of a suLtable hydrotreating catalys ~ :
sche~atically designated as 12. A hydrogen con~aining gas, for example,
a gas recovered from an olefin pla~t which containB~ for e:cample, 90 to 95 ~ ol
% hydrogen and remainder ~nethane, in line 10 i~ al~o introducsd into reacto
11, ~ accordance with the pre~erred embodiment, the total pressure Ln ~ ~ :
reaetor 11 is at a value which correæponds to the hydrogen gas supply pres~u e;:
for example, 400 psi~, thereby eliminatin~ the neceesity for the use of a :
booster compressor for the hydrogen gas ~eed. ~ reactor Il, as known in
the art, the pyrolysis gasoline i8 hydrogenat0d to selectively hydrol;reat the ,
diens~ and styrenes present in the pyrolysis gasolin~. :
A liquid hydrotreated e~fluent L~ wLthdrawn ~om reactnr 11 through .
. . line 16 and in~oduced into a s1:rLpping column I9 to separate the mo~e
. , ,
volatiLe components Irom the liquid effluent. The sb~ipl?er 1~ Ls operated at
a pressure lower than that prevalling in reaetor 11 in order to e~fect a sub-
stantinl flashmg of the mnre volatLle oomponent3 dinsolved in the llquid
effluent. : ~ ~
A gaseous effluent, coTItaining the excess hydroge~, is withdrawn from
reacl;or 11 t~ough lin~ 21 and pansed through condenser 22 to conden~ .
entrained hydrocarbons which are separated in ~eparator 23.
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~L0~7Z43 -
Hydrogen gas, lean of hydrocarbon~, ls withdrawn from ~epara,tor 23
through line 24 and lntroduced Lnto s~Lpper 19 a~ a ~trlpplng gas. .
The stripper 19 iB oper~ted at t~rnperatures and pre~sures to e~fect
the desirecl separatiorl of volatile hydrocarbon compon~nt~ by both flashing,
and strippLng with hydrogen gas recovered frorn the hydrotreatlng r~ac~r,
. The greater the a~nount of volatile c~nponents separated from the efflue~t
the higher the hydrogen partLal pressure whLch can be achLeved Ln reactor 11
As should be apparent, at the maxLmum, the t~tal amount of compon~qts whi h
can be stripped rvm the effluent correspond~ to the net efflucnt. ~crsas2d
removal o:E volatile components can be e~cted by a further decrea~e In the
pressure andtor an increase In the amount of hydrogen stI~Lppi~g gas. In
general, the stripping iB effected by the use of hydrogen stripping ga6 as
well as a pressure reduction to a pressure offrom 50 to ~00 p~LIess than
the pressure in reactor l1. The strippi~g ie generally effected at a temp~ra ~:
ture which correspond~ to the reactor outlet temperatura, i. e., no addltiona
~: ~ heating or cooling of effluent. ~
The stripping with hydrogen gas at an elevated temperature, in ~ ;
addition to offecting addlti~nal removal of vo~latile co~nponents from the efflul nt,
which increases hydrogen partial preBsure~ results in the further~advantagc
that hydrogen dissolvcs in the t~t liquid efilueslt thcreby providing partial ~ . :
:~ : recycle OI hydrogen gas with~ut a recycle compresBor~ In addition, ~uch
, ~ ,
recycle dlrectionally irnproves the hydrogen partial presslLre Ln reactor 1l, ;
:A ~tripped or lean hydrotreated effluent is withdrawn fro~ eolumn l0
t~ough line 31 and a portion thereoi recovered tbrough llne 32, as net produ t.
: The remaining portion in line 33 is cooled in exchanger 3~, a8 requlred, ~ ~ :
and eDtlployed as recycle in line 14. Aa hereinabove noted, tt~ u~e of a lean
recycle; i. e,, lean wLth respect to more ~rolatile compo~e~ts, reeults Ln
higher hydrogen partial pressures in reactor 11, at a given total prea~ure.
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~972~3
Th~ ~t;ripping ga~, contalning 9t:t~1ppet3. and flashed volatlle component~,
Ls wLthdrawn from co.lumn 19 through lLne 41, combin~d wlth separated liquL
in lin~ 42 from separator ~3, pa~sed throu~h conderlser 43, and introduced
Lnto fLash drur~l 44 to separate vapor and litauld. The flash drum 44
pre~rably operates at ~he pressure of ~LppLng column 19.
This vapor is rich In hydrogen and as such can be reused as rnake i~p
hydrogen to other hydrogenatlon reactions or It can be recycled to the
~lefins plant of origin ~or hydrogen and hydrogen recovery. Vapor ib r e
moved ~rom drum 44 through line 45. I.Lquid i~ withdrawn from drum 44
through line 46 and form~ a part of the net hydrotreated product. :
The hereinabove descrLbed embodiment may be rnodLfLed within the : ~ :
spirit and scope of the invention. Thus, ~or example, eparati~n of volatile
components can be effected other than as particu.larly de~oribed provided ~ :
that there i~ provided a leaned recycle which result~ In Ln~rea~ed hydrogen :
partial pressure. Similarly, It is possible to subject only the reoycle
portion of the ef~luent to the operation for sepæating the more volatile
components, rather ~han the entire effluent 8~1 described.
Sti.ll another modifLcatLon Lnvolvea separation of the volatile: com-
ponentæ from ~he effluent, wLt~ut s~ipping wLth hydrogen gas, as herein-
a~ter described with re~erence to Figure 2. ~
ReferrLng to Figu~e 2, aa described wLthrefèrence to the emhodiment ~:o~ Fig~e 1, pyroly~i~ gasolLne~ Ln line 113, leaned recycle e~fluent in lirl~
114 and hydrogen contaLnLng ga~ in line 110 are Lal~oduced into hydrotreatlrlg
reactor 111 includi~g a hydro~eating catabst bed 112, b~ sel~ctLvely
hydrotreat dL-olefin~ and ~tyrene~
A hydrotreated liquid effluent is wlthdrawn from reactor 111 through
line 116 and introduced into flashing column 201 operated at a temperature
and preseure to flash the more volatile componellt~ frorr~ the llq~id e~f~uent,
In columrl 201, separatLon o volatile component~ is effected by ~lashillg,
without addLtional stripping by the u~e of hydrogen containing ga~, a~
--~ ~7~1L3
described wîth reference to Figure 1, In general, colwnn 201 l8 oper~ted
at a pressure of from 50 to 200 psi lower than the reaction pressure, ~
described with reference to embodiment of Figure 1, As shoulà be a~parent,
a lower c~unount of less volatile components i,s ~eparated from the effluent
than is separated by proceeding in accordance with the embodlment of
Figure 1, which includes flashing and strippLng, whereby the ~rdrogen
partial pressures achieved in reactor 111 axe le~s tharl those achieved in
reactor 11 of Figure 1; however, the hydrogen partial pressures are greater
than those achieved by the use of conventionaL procedures.
;~ . The leaned liquid effluent is withdrawn fPom column 201 through line
. 202, with a first portion being recovered as net product in line 203, and a :
second portion being recycled to the hydrotreating reactor through line 133
including cooler 134.
A vapor effluent is withdrawn :from reactor 111 through line 204, and
combined with flashed vapors from column 201 m line 206, ~or passage
through condenser 143 for introduction in~o flash drum 144, which preferably ~
operates at the pressure of coiumn 201, ~ ~:
Va~or is withdrawn from drum 144 through line 145. ~ Liquid is
withdrawn from druxn 144 through line 146, and forms part of the net produc
¦ The present invention will be further illustrated with resp~ct to the -
iollowing ex: le:
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~ ~IL097Z43
EXA~IPL~
The following are Ulustrative conditions for the hydrotreQtlng of
pyrolysis gasoline in accordance with the embodi~nent o:E Figure 1:
Line 1 Q~ 1~ ~ ll 6 . 21 24 41 _ _
~empF 100 100 380 335 4ooo 4ûO" 100 395
, __ ~ _ . _ _~
Pressure, psia 400 450 45û 400 410 400 260 250
. ~ _ , . _ _ . . - __ .
Flow rate 58 115 420 535 519 4~ 186 92
moles/hr . .
, _ , __ _
. Mol ~o o~ C5 _~ 23 B. 0 11. 213. 0 __ _ _ __
. and lighter .
_ ~ _ _ __ . _ _
Mol % of H2 95 -- -- -- __ 42. 8 90 23. 0
. .'
The present invention is particularly advantageous in that the hydrogen
partial pressure in the pyrolysis gaso~ine hydrotreating rPactor can be
increased, thereby permitting the use cf lower total reaction press1lres,
while slmultaneously deri~ring the improved kinetics reæulting from ~uch
higher hydrogen partial pressure. The ability l;o use lower total pressure~
ellminates the necessi1:y for booster compressor for the hydrogen rontaining
gas. T~s, by proceeding in accordance with the inventLon it ie poe~ible k):
operate the h~drotreating reactor at the delivery pressure of the a~llable
hydrogen containing gas at hydrogen partial pre~ sure s which are gr~ater
than those which can be achieved by proceediDLg in accordance with converl-
tionai proce es,
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